The present invention relates to a torch for cutting, welding or heating metals, and more preferably a cutting torch to which the pressure fluid to be used is fed at the highest possible pressure.
For starting a cutting operation, for example, torches are ignited by matches, lighters or like manual devices which are prepared separately. However, when torches, especially those adapted to be held by hand, are to be ignited by such a manual device, the igniting device must be manipulated by one hand with the torch held by the other hand, while a valve must be opened to discharge a combustible gas from the nozzle end for ignition. Thus the overall igniting procedure is very cumbersome. Moreover there is the likelihood of an ignition failure or explosive ignition, or the hazard of causing a burn to the user, depending on the timing and amount of the discharge of the combustible gas.
To overcome these problems, torches have recently been proposed which per se are provided with an automatic igniting device comprising a piezoelectric assembly. Effectively utilizing the pressure energy of the pressure fluid used, the piezoelectric assembly is operated to generate a high voltage, producing a spark at the nozzle end with the electromotive force and automatically igniting a combustible gas flowing out from the nozzle end. A typical example of such torches is disclosed in Published Unexamined Japanese Patent Application No. 68712/1981.
Briefly stated, the disclosed torch, which is designed for cutting, has a nozzle replaceably attached to the head thereof and provided in a fluid channel therein with a piezoelectric element, a striker therefor, a magnet for attracting the striker, lead wires extending to spark electrodes at the forward end of the nozzle and other related parts needed for producing sparks. When valves on pipes for feeding a combustible gas and preheating oxygen gas are opened, the striker in a standby position as held attracted to the magnet is forced away therefrom into percussive contact with the piezoelectric element by the pressure of the resulting combustible gas mixture to generate a high voltage, producing a spark across electrodes at the nozzle end to which the electromotive force is delivered through the lead wires and automatically igniting the combustible mixture flowing out from the nozzle end. Thus the torch can be automatically fired only by opening the valves which are invariably opened for starting a cutting operation. The torch can therefore be ignited much more easily by the above device than by the manual devices conventionally used. The device further has another advantage that the torch can be ignited reliably with proper definite timing at all times.
The disclosed device nevertheless has various drawbacks. The nozzle, which has many parts incorporated therein, is very complex in construction, cumbersome to make and assemble and extremely costly. The pressure of the combustible gas mixture fed is not sufficiently high, while the size of the piezoelectric element is limited by the size of the nozzle, so that the electromotive force is smaller than is desired, consequently entailing the likelihood of ignition failures. Although it appears possible to utilize the pressure of a flow of high-pressure cutting oxygen gas to increase the fluid pressure to be applied to the piezoelectric element, the parts then incorporated in the internal channel of the nozzle for the oxygen gas will impede and disturb the gas flow to result in a reduced cutting efficiency. Moreover, whether the channel having the piezoelectric element incorporated therein is the combustible gas mixture channel or the cutting oxygen gas channel, the element, the magnet, etc., which are positioned close to the fire, tend to become thermally deteriorated early due to the conduction of heat through the nozzle itself. In addition, the nozzle is relatively small generally, most susceptible to the influence of heat and therefore liable to become damaged early. In such an event, the nozzle must be removed from the torch head and replaced by a new one. Thus the nozzle is to be handled as an expendable. The arrangement wherein the automatic igniting device is incorporated in such a nozzle has the drawback of inflicting a great economical loss on the user.